fun readInt () =
    valOf (TextIO.scanStream (Int.scan StringCvt.DEC) TextIO.stdIn)


val () =
    let
        val n = readInt ()
        val ws = Array.tabulate (n, fn _ => readInt ())
        val sum = Array.foldl (fn (w, acc) => w + acc) 0 ws
        val dp = Array.array (n * 100 + 1, false)

        fun doDp () =
            (Array.update (dp, 0, true);
             Array.app (fn w =>
                           let
                               val i = ref (n * 100)
                           in
                               while 0 <= !i do
                                             (if Array.sub (dp, !i)
                                              then Array.update (dp, !i + w, true)
                                              else ignore ();
                                              i := !i - 1)
                           end
                       )
                       ws)
    in
        if sum mod 2 <> 0 then print "impossible\n"
        else
            (
              doDp ();
              if Array.sub (dp, sum div 2) = true then print "possible\n"
              else print "impossible\n"
            )
    end